The existence of a dietary requirement for fatty acids of the Omega3 or Alpha-linolenic acid family remains an unresolved issue in human nutrition. Like the Omega6 or linoleic acid family, Omega3 fatty acids cannot be synthesized by animals. The high content of Omega3 fatty acids in the retina and cerebral cortex suggests an important role in the function of neuronal and photoreceptor membranes. Previous studies of dietary deficiency of Omega3 fatty acids in rats demonstrated tissue depletion of Omega3 fatty acids, reduced electrophysiological responsiveness of the retina, and impaired learning ability. We propose to complete a long-term study of dietary deficiency of Omega3 fatty acids in nonhuman primates. Adult female rhesus monkeys are fed one of two semipurified diets for at least two months before mating and throughout pregnancy, and their infants then receive similar diets from birth to one year. The experimental diets, with fat supplied by safflower oil, have a very low content of Omega3 fatty acids; the control diets - identical except for the fat source, soybean oil - have a relatively high content of Omega3 fatty acids. Using biochemical, electrophysiological and behavioral techniques, we are monitoring the fatty acid composition of plasma and tissues and are testing the infants' visual function and learning ability. To date, levels of Omega3 fatty acids have fallen significantly in all plasma lipid classes of the experimental group's adult females and are nearly undetectable in the infants' plasma lipids. Skin and adipose tissue biopsies from the experimental infants also contain significantly reduced proportions of Omega3 fatty acids. Thus, the experimental diet has produced severe depletion of Omega3 fatty acids. A behavioral test of the infants' visual function demonstrated that the development of visual acuity was significantly impaired in the experimental group. The ability of the infants to learn a spatial reversal task, however, was not affected. Electroretinogram recordings and further tests of visual function are in progress. During the proposed two year renewal we plan to achieve the desired number of infants in both diet groups and to complete testing of visual function and behavior. At one year of age tissues, including retina and brain, will be examined for lipid and fatty acid content and for histological changes.